The present invention concerns a process and devices for the catalytic treatment of a fluid charge, and more particularly, for hydrocarbon conversion or hydroconversion.
The invention is particularly applicable to the catalytic treatment of liquid charges such, as for example, heavy crude oils, vacuum residues of hydrocarbons distillation, these treatments being generally effected in the presence of hydrogen and/or gaseous mixtures of high hydrogen content, over a bed of a solid catalyst, the catalyst being used as particles (extrudates, particles of various shapes, balls etc.).
In such catalytic treatments, a quick deactivation of the catalyst is often observed as the effect of catalyst poisons, coke formation, fouling by certain metals, etc.
This deactivation requires the frequent replacement of a portion or the entire catalyst bed.
According to the invention, the catalyst withdrawal from the reactor is effected progressively. The term "progressively" means that the catalyst may be withdrawn:
either periodically, for example, at a frequency from 1/10 to 10 days, while withdrawing at each time only a fraction, for example from 0.5 to 15%, of the total catalyst amount. It is possible, according to the needs, to withdraw a greater catalyst amount, for example up to 100% of the total catalyst amount, i.e. the totality of the catalyst. The catalyst withdrawal frequency may be higher (periodicity of the order of 1 minute or 1 second for example), the withdrawn amount being accordingly reduced. Between two withdrawal periods, the reactor thus operates with a fixed bed. PA1 Or in a continuous manner; in this case, the reactor is of the movable bed type. The fresh catalyst is introduced at the upper portion of the reactor and the process and the devices for removing the used catalyst at the lower portion of the reactor through a withdrawal funnel, are the object of the present invention.
The process according to the invention and the devices of the invention are also convenient for withdrawing catalyst particles from reactors for the cracking, hydrocracking, hydroreforming, aromatic hydrocarbon manufacture, paraffinic, naphthenic or aromatic hydrocarbon isomerization, the various reactions of hydrogenation, dehydrogenation, alkylation, transalkylation hydrodecyclization, hydrodealkylation, etc. reactors wherein the injected charge and/or gases flow upwardly. The device and the process according to the invention are also convenient for all the vessels where are handled liquids and/or gases as well as solid, powdered particles, irrespective of their size, provided that they may flow downwardly by gravity effect or by means of a controlled gas leak driving these particles. Non limitative examples of said particles are: gravels, sands, balls, grains, granules, tablets, pellets of any kind used in pharmacy, confectionary, food industry, etc.
Preferably, the fluid charge is introduced into the particles containing reactor or enclosure through distribution means located at the lower part of the reactor or enclosure and circulates countercurrently with the catalyst or the particles before being discharged, after treatment, from the upper part of the reactor (or the enclosure which will be arbitrarily called "reactor" in the description hereinafter).
The flow of the catalyst or particles, by gravity, ensures the regular lowering of the catalyst bed or of the particles bed (particles which will be called arbitrarily "catalyst" in the description hereinafter), whereas the upward circulation of the fluid charge makes possible, in particular, to easily adjust the residence time and to provide a continuous fluid phase.
Furthermore, the countercurrent circulation of the charge and the catalyst makes it possible to obtain a more complete catalytic conversion since the fresh catalyst introduced at the top of the reactor treats an almost already converted charge (i.e. essentially containing compounds whose conversion is difficult), whereas, at the reactor bottom, the used catalyst treats a fresh charge (i.e. a charge having a high content of compounds easy to convert), thereby efficiently effecting the first steps of the conversion. This results in a systematic use of the catalyst in the reactor, a more regular thermal gradient of the catalyst bed than with a circulation of the co-current type, with, in particular, at the bottom of the reactor, a more moderate temperature reducing the probability of catalyst coking.
A catalytic conversion process with a movable bed is taught in U.S. Pat. No. 3,826,737. This process is, however, more particularly adapted to the co-current circulation of the catalyst and of the liquid charge, the latter being discharged at the reactor bottom through a cylindrical grid placed at the bottom of the catalyst discharge cone.
This process has the disadvantage resulting from the possibility of clogging of the grid by the catalyst particles pushed against the grid by the liquid charge discharged from the bottom of the reactor. There may result therefrom an uneven distribution of the fluid through the catalyst, a difficult flow of the catalyst bed, with the possibility of blocking certain zones of the bed, as well as an increase of catalyst abrasion due to the friction between blocked particles and the free particles of the catalyst bed, and between free catalyst particles and the grid for the discharge of the liquid charge.